(a) Field of the Invention
The present invention relates to a call processing signal routing system in a local exchange system, and more particularly, to a call processing signal routing system for transferring a call processing signal in a signaling system, such as ISDN or No. 7 common signaling system.
(b) Description of the Related Art
Conventional signaling systems, such as ISDN or No. 7 common signaling system, generally comprises a central processor in a local exchange system of a routing station for receiving a call processing message. FIG. 1 is a schematic block diagram for showing the configuration of a local exchange system of a routing station and the signal flow of the call processing signal therein.
The local exchange system comprises a time-division switch 11, a central processor 12, trunks 13 and 15, and common signal equipment (CSE) 14 and 16. Trunks 13 and 15 are connected to respective nodes corresponding to other local exchange systems through transmission lines 20 and 21. The common signal equipment 14 or 16 controls data in the data link layer, and the central processor 12 controls data in the network layer. When a call processing message arrives through transmission line 20, for example, common signal equipment 14 extracts the call processing message from trunk 13 to transfer the same to central processor 12.
Central processor 12 operates by itself for routing the received signal if the message is addressed to the own local exchange system. On the other hand, if the message is addressed to another node or another local exchange system, the message is transferred through common signal equipment 16 to corresponding trunk 15, and then to the specified node outside the station. In this system, all the routing processing in the exchange system is performed by the central processor 12, which causes a heavy load to the central processor 12.
Some proposals are made to alleviate the load of the central processor, wherein the common signal equipment has a function for processing signal routing by itself to alleviate the load of the central processor. In this system, each common signal equipment stores routing information (address) for the own station, and judges whether or not the routing information in the received signal coincides with the stored routing information.
If it is judged that the received routing information coincides with the stored routing information in the common signal equipment, then the received data is transferred to the central processor for processing the received data in the own station. If not, the received routing information is transferred to the central processor for further routing processing to thereby select the transmission line for the message. By using the proposed system, the data transfer between common signal equipment and the central processor is reduced to some extent to thereby alleviate the load of the central processor.
In the proposed system, however, if the received routing information does not coincide with the stored routing information, the central processor further operates for routing processing, resulting in limited load alleviation of the central processor, with limited reduction of the routing processing time.